Molecular and enzymatic properties of fibrinoligase (i.e., thrombin and calcium ion activated blood coagulation Factor XIII) will be intensively studied. Differential diagnosis of a number of hemorrhagic conditions in the family of disorders of fibrin stabilization will be perfected. BIBLIOGRAPHIC REFERENCES: "Endo-gamma-Glutamine:epsilon-Lysine Transferases, Enzymes Which Cross-Link Proteins", L. Lorand and P. Stenberg, Hdbk. of Biochemistry and Molecular Biology, Proteins Vol. II, 3d ed. (G. D. Fasman, ed.), pp. 669-685, CRC Press, 1976. "Fibrin Stabilizing Factor (Factor XIII)", C. G. Curtis and L. Lorand, Methods in Enzymology, 45, Academic Press, p. 177, 1976, in press.